The present invention relates to an assembly for mounting a boarding ladder on a machine to allow movement of the ladder to either a raised storage position or a lowered boarding position.
Boarding ladders are required in a wide variety of installations such as, for example, on large excavating machines used in mining. The ladder is mounted on an excavator so that it can be pulled down to a lowered boarding position to enable the operator to climb onto the excavator, after which the operator must pull the ladder up to a raised storage position to allow operation of the excavator without damage to the ladder. Such ladders can weigh 165 lbs. or more and therefore it is necessary to provide some type of lift-lower assistance in the ladder mounting assembly to aid the operator in raising and lowering the ladder.
Boarding ladder assemblies generally include two types of lift-lower assistance: counter balancing spring mechanisms and counter weight mechanisms. With both types of lift-lower assistance it is necessary to mechanically secure the ladder in its raised or lowered position by some type of latching mechanism. Boarding ladders are normally of such a length that it is impossible for the operator to activate the latch mechanism from both the top and the bottom of the ladder without some type of latch actuating linkage that extends so as to be accessible from both the top and the bottom of the ladder. Such latch mechanisms are expensive to manufacture and are prone to malfunction or breakage. If the latch mechanism becomes inoperative, the ladder cannot be held in its raised or lowered position. This interferes with the operation of the excavator. Further, latch mechanisms are disliked by operators because the latching and unlatching operation takes time.